The present invention relates in general to communication systems and components therefor, and is particularly directed a power supply interface circuit that is configured to prevent a circuit path of telecommunication equipment, such as a telephone line test device, containing an circuit interruption device (such as a fuse or circuit breaker), from being subjected to an improper (reverse) connection to a power source therefor (such as a primary power source and an auxiliary battery), so that the circuit interruption device will not be tripped thereby. In addition, the inventive interface circuit includes an indicator circuit that is operative to indicate whether the device""s power terminals are properly connected to each power source, so that, if inadvertently reverse-connected, the wires can be properly reconnected, and thereby provide for delivery of power to the device from either power source, as required.
Users of telecommunication system equipment often install one or more auxiliary devices, such as but not limited to test units and the like, at either or both of host (central office (CO)) and remote (customer premises) sites of the system. In addition to being interfaced with communication links of the system proper, these devices must be properly powered. In some instances, the power may be drawn from the same wires used to send voice and/or data over the telephone lines. This type of powering, which is sourced from a CO battery (xe2x88x9248 VDC and ground (GND)), is commonly referred to as xe2x80x98loopxe2x80x99 or xe2x80x98spanxe2x80x99 powering, and permits the phone company to remotely power equipment that may be located up to several miles from the central office.
Within the telephone networks of the continental United States, loop powering is used extensively on mid-span devices (rather than termination devices) in DDS, ISDN, T1, HDSL, and other digital networks. Terminating devices for digital data services are generally not span-powered; instead, being typically located within the customer""s premises, they receive power from the customer""s local utility feed. In addition, the auxiliary device may not continuously require span-supplied power, or it may use this power only during emergency situations.
Where the auxiliary device is powered from a local utility, as in the case of equipment installed at the customer""s premises, a loss of local power (for example during a lighting storm) will cause the terminating device to stop functioning. This is problematic for digital services (such as ISDN) that implement plain-old-telephone-service (POTS) support. Thus, a local power failure will cause a loss of phone service (including emergency service, such as the ability to place a 911 call). As a consequence, digital service customers have traditionally been required to maintain a separate standard analog phone line, in addition to the digital data line(s).
Irrespective of the need to provide auxiliary POTS service, the type of equipment employed, or whether the equipment is located within the central office or at a remote site, it has become common practice to employ multiple (dual) power feeds, one serving as a primary supply, and the other providing an auxiliary back-up. These two feeds typically include a CO battery, as well as an auxiliary DC supply, that are xe2x80x9cORxe2x80x9d-fed to the auxiliary circuit of interest through a circuit interruption or protection device, such as a fuse or circuit breaker. Unfortunately, during installation of the equipment, it sometime happens that one or both pairs of power supply leads are miss-wired (reversed)xe2x80x94resulting in triggering the operation of the protection device (i.e., tripping the circuit breaker or blowing the fuse).
In accordance with the present invention, this problem is effectively obviated by a new and improved power supply interface circuit, that is configured to prevent the power supply path to the telecommunication circuitry, which contains a circuit interruption or protection device, from being subjected to an improper (reverse) connection of the device""s power terminals to one or more power sources. In addition, the invention contains a polarity indicator circuit that is operative to indicate whether the device""s power terminals are properly connected to a power source, so that if inadvertently reversed, the wires can be properly reconnected, and thereby provide for delivery of power from either power source, as required.
For this purpose, respective sets of power supply connection terminals are provided to allow connection to respectively different sources (e.g. a primary (CO) supply and a back-up supply) capable of providing operational power for the telecommunication circuit. Each set of terminals includes one terminal to be coupled to the relatively positive power supply voltage (e.g., ground) and a second terminal to be coupled to the relatively negative power supply voltage (xe2x88x9248 VDC).
Each set of power supply terminals is connected to respective nodes of the power supply circuit path through diodes, which are forward conducting for only a proper polarity connection of the power supply connection terminal to a respective power source, but prevent the protection device from being triggered in the event of an improper (reverse) connection of either set of power terminals to its associated power sources.
In addition, to indicate whether the power supply terminals are connected to the proper polarity supply voltage, a polarity indicator circuit, containing one or more light emitting diodes, is coupled across each set of power supply connection terminals.